1. Field of the Invention
The present invention relates to a surface-emitting laser device, and more particularly to an improved surface-emitting laser device by which a continuous oscillation can be made at room temperature by junction-growing an AlAs/GaAs lower portion reflector having a high reflective index and an InAlAs/InGaAs upper portion reflector having a high lattice mismatch.
2. Description of the Conventional Art
The thin film material of a 1.5 micron laser device is directed to forming an InP substrate and depositing an InGaAs/InGaAsP mutilayer thin film of an InP group on the InP substrate. Recently, an InGaAs/InAlGaAs thin film growth method was performed in the industry. The basic construction of the surface-emitting laser device includes a lower reflector formed on the substrate, an activation layer, and an upper reflector.
In one reflector, the reflective index should be 1 at 1.5 micron, and in another reflector, the same should exceed 0.95.
As the reflector, the distributed Bragg reflector using the refractive difference of the ultralattice thin film structure has the best quality.
However, since the semiconductor reflector of the InP group has a small reflective index difference at 1.5 micron band, an optical wavelength band, the thin film thickness of the reflector having the reflective index of 1 is very thick.
The surface-emitting laser device having a thick reflector has a high resistance characteristic, and a high heat generation rate, and degrades the quantum efficiency.
Meanwhile, since the AlAs/GaAs thin film reflector of a GaAs group has a high reflective index and is thin, it is adaptable to 1.5 micron, however when the activation layer of the InP group is grown thereon, since the lattice mismatch is 4.2%, the optical characteristic of the activation layer is degraded.
As another junction method, there is a method for bonding the lower reflector of the GaAs group with the activation layer of the InP group at a high temperature. However, a characteristic degradation appears due to the high temperature process.
The Si/SiO.sub.2 which is a dielectric material, or an AlGaSb/AlSb ultralattice reflector of the antimony both have a high refractive index, so it is possible to get a high reflective index at the thin layer.
However, the dielectric thin film has a low heat transfer rate, so it is difficult to practically use it in the industry. In addition, the antimony group is a new material, however more studies are necessary.
The surface-emitting laser device of 1.5 micron band width is one of ideal optical devices in the optical fiber communication, and the cost is not high.
In addition, parallel type optical communication using two dimensional arrays is capable of processing a large amount of information, so it becomes a major technique for the optical logic device and can be adapted for an optical digital computer.
The commercial use of this device can be substituted for the use of the expensive cross-section-emitting laser, and with its low cost, it may be used for home-based optical communication.
The laser device which is fabricated in the lattice structure requires a technique for developing a new thin film material and bonding heterogenous structures which have a different lattice constant since the laser device has a low reflective index characteristic.
However, in the industry, a more economic surface-emitting laser device which continuously oscillates at room temperature has not been introduced.